A measuring system is being developed for pressure gradient determination at critical sites in the arterial system. This is to be computer corrected, and correlated with theoretical dynamic models of blood flow at these sites. A computer model of arterial blood flow is being developed for arbitrary time-varying input, arbitrary blood viscosity profile, and fairly general geometry. It furnishes the velocity pressure and shearing-stress profiles and time distributions. A computer model is developed which gives a two dimensional concentration max of a diffusing substance (e.g. cholesterol) in endothelial (or other) tissue for arbitrary boundary conditions. It includes the effect of partially impermeable surface barriers, if any.